...
Motivation: Important satellite missions, amongst which are USA, Chandra, and CGRO, have had problems with the absolute times assigned to events. See the anecdotes at the end of the page. The 10 uS timing precision required for the GLAST LAT is _essential_for good pulsar science. In addition to extensive testing of the different links in the timing chain, we have proposed an end-to-end test which will be the main focus of this page.
...
Using FSW muons acquired at NRL on 27 May, 2006 (run 77005390) I practiced how I plan to analyse the data we'll acquire. Here is the output plot:
At left is cos(theta)sin(phi) vs cos(theta)cos(phi) for those of the first 13000 events having exactly one reconstructed track. I faked a corresponding list of VME GPS time stamps from the muon telescope by taking the LAT times and adding1 µS per event to them (an implausible and catastrophic scenario intended mainly to give some grist to my code). I then pretended that the scintillator paddles were at the place in space corresponding to the spot in the middle plot, which I reconstructed by requiring <100 µs between the LAT time and my fudged time. Note the presence of a few accidentals. Finally, in the plot on the right, I made a spatial cut and plotted the time difference (for a larger sample than for my training sample).
Since the May data had a fair number of strangenesses in the ContextLsf variables, I re-ran the code for some post-TVAC "door open" data from GMT 2006-09-08 11:13:43 (run 77010099). The detector is horizontal. The left-most plot is amusing, I didn't fill the other two. I can explain the funny structure -- can you?
As for the weirdnesses -- they didn't reappear. I spoke with Anders, he said "FSW hasn't changed between the two data sets, those bugs are known and sporadic, you were just lucky on the recent data". Last but certainly not least: here is my code in a gzipped tar file.
Background material:
Links to science requirement document ; to measurements made by J.G. Thayer ; to measurements plot and text made by G. Godfrey ;
Presentation to Spectrum (General Dynamics) made at 22 August I&T meeting by Neil Johnson, prepared by David Smith.
...